Ground Motions and Structures - Earthquake Engineering for Structural Design - page 377

Ground Motions and Structures 377

supply system. Some historical records show that small fires are often initiated by
earthquakes and they sometimes grow into large destructive fires, causing loss of life
and severe damage to properties. The main concern is initially related to the damage to
individual wooden buildings. A subsequent concern is the possibility of devastation
resulting from a large urban conflagration. The factors affecting the probability that
small fires could grow into large fires include: the amount of earthquake damage, the
type and density of building, the wind conditions, the loss of water supplies and the fire
fighting capabilities (Botting and Buchanan, 2000).
The fire conflagration following the 1906 San Francisco earthquake significantly
exceeded the shake losses and resulted in the largest earthquake loss in American
history. Similarly in Japan, the fire losses following the 1923 Great Kanto earthquake
were much larger than the shake losses (Mortgat et al, 2004). Recently, during the 1994
Northridge and 1995 Kobe earthquakes, a great part of losses were attributed to fire the
following earthquake.
According to the modern seismic design, ordinary structures are designed to suffer
damage to some extent during strong earthquakes, exploiting their own structural
ductility to avoid collapse and to safeguard human lives. The problem of fire following
earthquake consists in the fact that the fire coming soon after an earthquake will find an
already damaged structure, which is more vulnerable than the initial undamaged one.
Therefore, the danger of global collapse due to fire for the damaged structure increases.
The collapse risk depends on the extent of the earthquake damage, because the fire
resistance rating of the structure could be significantly reduced. The conditions that the
rating reduction is under 10% ( which is considered as negligible) for steel structures
are examined by Della Corte et al (2003a,b): (i) The reduction of fire resistance due to
seismic damage is negligible for moment resisting frames, which are designed
considering the serviceability seismic requirement at the design seismic intensity level:
(ii) For earthquakes having intensity larger than the design value and/or structures not
adequately designed against earthquakes, the fire resistance reduction could be
significant and should be taken into account.

8.8 REFERENCES

Adams, W. (2004): Planning buildings to resist earthquakes. Joint Technical Session
between Jamaica Institution of Engineers (JIE) and Carribean Division of Institution of
Structural Engineers (UK), December 2004
AISC (2006): Seismic provisions for structural steel buildings. Commentary
ASCE 7 (2005): Chapter 5. Structural Design Criteria. Commentary.
Astaneh-Asl, A. (2003): Progressive collapse prevention in new and existing
buildings. Emerging Technologies in Structural Engineering. Abu Dhabi Conference,
1001-1008
Avram, C. Facaoaru, I., Filimon, I., Mirsu, O., Tertea, I. (1981): Concrete Strength
and Strains. Elsevier Scientific Publishing Company, Amsterdam